R-type Calcium Channel Isoform in Rat Dorsal Root Ganglion Neurons

ABSTRACT

R-type Cav2.3 high voltage-activated Ca2+ channels in peripheral sensory neurons contribute to pain transmission. Recently we have demonstrated that, among the six Cav2.3 isoforms (Cav2.3a~Cav2.3e), the Cav2.3e isoform is primarily expressed in trigeminal ganglion (TG) nociceptive neurons. In the present study, we further investigated expression patterns of Cav2.3 isoforms in the dorsal root ganglion (DRG) neurons. As in TG neurons, whole tissue RT-PCR analyses revealed the presence of two isoforms, Cav2.3a and Cav2.3e, in DRG neurons. Single-cell RT-PCR detected the expression of Cav2.3e mRNA in 20% (n=14/70) of DRG neurons, relative to Cav2.3a expression in 2.8% (n=2/70) of DRG neurons. Cav2.3e mRNA was mainly detected in small-sized neurons (n=12/14), but in only a few medium-sized neurons (n=2/14) and not in large-sized neurons, indicating the prominence of Cav2.3e in nociceptive DRG neurons. Moreover, Cav2.3e was preferentially expressed in tyrosine-kinase A (trkA)-positive, isolectin B4 (IB4)-negative and transient receptor potential vanilloid 1 (TRPV1)-positive neurons. These results suggest that Cav2.3e may be the main R-type Ca2+ channel isoform in nociceptive DRG neurons and thereby a potential target for pain treatment, not only in the trigeminal system but also in the spinal system.